In many electronics applications, it is desirable to increase the voltage of a power source to a higher voltage. A charge pump is a common circuit for increasing the power source by some multiple. Charge pump circuits are used to drive the gates of field effect transistors to voltage levels in excess of supply rail voltages. Typically, such circuits have been used to drive MOSFET transistors that switch power to electronic loads (e.g., load switches). For example, in portable computer applications, MOSFET power transistors are used to switch peripheral devices such as disk drives and displays. In such and other applications, the peripheral device is coupled to the source of the MOSFET switch while the MOSFET's drain is coupled to the supply rail. When a MOSFET switch is coupled in this way, it is desirable to drive the gate of the switch at voltages in excess of the supply rail voltage in order to fully turn on and enhance the switch.
Charge pump circuits used to drive MOSFET switches typically employ oscillators in conjunction with a small number of capacitors to multiply or boost the supply rail voltage to a higher gate voltage. In many applications, the power consumed by this type of circuit can be quite large due to the power consumed by the load and the load switch. Thus, the power efficiency of the load switch is generally of concern since in some battery-powered applications (such as mobile electronic devices, e.g., notebooks, cellular phones, electronic pads, etc.) power efficiency is very important. In these applications, the power efficiency of the load switch may be a factor in determining battery drain and, hence, battery life before recharging or replacement of the battery becomes necessary.
In view of the foregoing, it would therefore be desirable to provide a power efficient load switch which can rapidly multiply or boost a supply rail voltage so as to drive the gate of a load switch at a voltage in excess of the supply rail voltage and can be optimized to minimize quiescent-current loss.